The invention relates to a DC/DC converter circuit including a voltage conversion circuit which in active operation is able to convert the input voltage of the DC/DC converter circuit into an output voltage of the DC/DC converter circuit differing from the input voltage, a regulator circuit for regulating the output voltage to a predetermined design value, the regulator circuit comprising a reference voltage generator circuit and a comparator, at the first input of which a voltage characterizing the output voltage and, at the second input of which the reference voltage generated by the reference voltage generator circuit is available and which outputs a control signal for activating/deactivating the voltage conversion circuit as a function of MIN/MAX violation of the design value by the output voltage.
One such DC/DC converter circuit is known from prior art and reads e.g. from the background description of the U.S. Pat. No. 5,680,300 (xe2x80x9cRegulated charge pump DC/DC converterxe2x80x9d). The voltage conversion circuit of the described DC/DC converter circuit comprises a charge pump circuit.
One disadvantage of the circuit as described at the outset is that when the current requirement at the output of the circuit is relatively small or zero, e.g. in standby operation, a relatively large current consumption materializes. This is due to the fact that the regulator circuit itself, i.e. the reference voltage generator circuit and the comparator continue to consume current. When a bandgap reference is used as the reference voltage generator circuit a voltage divider may furthermore be provided which divides from the output voltage a voltage which is adapted to the reference voltage and applied to the first input of the comparator as the voltage characterizing the output voltage. The voltage divider too consumes current when the DC/DC converter circuit is on standby.
To reduce the standby current consumption of such circuits, i.e. when the output of the circuit has no or very little current consumption, a DC/DC converter circuit is proposed by Linear Technology in its DC/DC converter LTC151G in which a change is made from standby to normal operation by a signal applied to the circuit from without. This circuit was described on the homepage of Linear Technology available e.g. on Jun. 10, 2000 under the address xe2x80x9cwww.linear-tech.comxe2x80x9d. The signal for making the change from standby to normal operation is furnished to the DC/DC converter circuit by a microprocessor. In this arrangement an ON pin of the circuit receives during standby a signal with a high duty cycle (e.g. 95 to 98%) adapted to the max. standby current of e.g. 100 xcexcA as established prior by relating the max. permissible OFF time for this standby current to the mm. ON time in determining the duty cycle. When the ON time is e.g. 0.2 ms and the max. permissible OFF time is 10 ms the circuit consumes current only during 2% of the ON time during standby as compared to normal operation.
One disadvantage of the circuit as described is that it cannot automatically make the changeover between normal operation and standby. Another disadvantage is that during standby the ON/OFF ratio is fixed and not adapted to the actual current consumption required at the output of the DC/DC converter circuit at any one time which results in a relatively high standby current consumption of the DC/DC converter circuit.
Referring now to FIG. 1 there is illustrated by way of a block diagram a prior art DC/DC converter circuit wherein the modules 1, 2, 3, 4 and 5 usually grouped together into an integrated circuit are illustrated boxed.
The known DC/DC converter circuit comprises a voltage conversion circuit which in this case consists of a charge pump circuit. The charge pump circuit consists of a charge pump capacitor Cpump, an output stage 1 comprising the controllable switches of the charge pump and connected to the input voltage Vcc of the circuit, and a control circuit 2 including oscillator and driver for signaling the controllable switches which may be MOS-FETs, for example. The control circuit 2 receives its current from the input voltage source Vcc. In active operation the control circuit 2 controls the switches of the charge pump circuit cyclically so that the charge pump capacitor is firstly switched in a first phase so that it is charged to the input voltage Vcc of the DC/DC converter circuit and then in a second phase is switched so that it is in series with the input voltage Vcc so that at the output of the circuit a voltage materializes which is higher than the input voltage Vcc and at the most may correspond to roughly twice the input voltage Vcc. Such charge pump circuits capable of converting an input voltage into a higher, lower or inverted voltage at the output are known in prior art as described e.g. in the text book xe2x80x9cThe art of electronicsxe2x80x9d by Paul Horowitz and Winfried Hill, 2nd edit., Cambridge University Press, 1989, page 377 et seq.
The known DC/DC converter circuit comprises furthermore at the output a storage capacitor Cout on which the output voltage Vout of the circuit is stored. Connected in parallel thereto is a resistor R1 indicated in FIG. 1 symbolizing the load applied to the output of the DC/DC converter circuit.
In addition, the known DC/DC converter circuit comprises a regulator circuit consisting of a comparator 3, a bandgap reference voltage generator circuit 4 and a voltage divider 5.
In this arrangement the comparator 3 receives at its first input 6 part of the output voltage Vout of the DC/DC converter circuit divided by the voltage divider adapted to the reference voltage Vref generated by the bandgap reference voltage generator circuit applied to the second input 7 of the comparator.
The comparator, whose output is connected to the control circuit 2, regulates the output voltage of the DC/DC converter circuit by the skip-mode principle to a predetermined design value by it outputting a control signal to activate, and a control signal to deactivate, the voltage conversion circuit (1, 2, Cpump) as a function of MAX/MIN violation of the design value by the output voltage Vout of the DC/DC converter circuit so that the charge pump circuit is only ON in MIN violation of the predetermined design value by the output voltage Vout.
As already described above, the circuit as shown in FIG. 1 has the disadvantage that it has a relatively high current consumption since the regulator circuit is also ON when the circuit is on standby, it being the comparator in actual practice which consumes the most current (e.g. Icc=20 xcexcA) followed by the reference voltage generator circuit (e.g. Icc=10 xcexcA) and the voltage divider (e.g. Icc=6 xcexcA).
An aspect of the present invention is to provide a DC/DC converter circuit which overcomes the cited disadvantages and features a lower standby current consumption as compared to prior art circuits of this kind.
This aspect is achieved by a DC/DC converter circuit as cited at the outset in which the DC/DC converter circuit additionally comprises a circuit for signaling the regulator circuit ON/OFF comprising a comparator, at the first input of which a further voltage characterizing the output voltage and, at the second input of which a voltage at a capacitor is applied, and a control circuit comprising one or more controllable switches, the control circuit receiving the control signal of the comparator of the regulator circuit and the output signal of the comparator of the circuit for signaling the regulator circuit ON/OFF as well as outputting a signal(s) for controlling the switch(es) during the ON time of the regulator circuit controlling the switch(es) so that the capacitor is connected by a voltage defined by the regulator circuit so that it is charged to a voltage which differs by a predetermined amount from the voltage characterizing the output voltage, and when it is signaled by the comparator of the regulator circuit that the voltage has attained the design value it outputting the signal for signaling OFF the regulator circuit and controlling the switch(es) so that the capacitor is separated from the charging voltage so that it is gradually discharged, the comparator of the circuit for signaling the regulator circuit ON/OFF outputting a signal to the control circuit when the further voltage characterizing the output voltage and the voltage across the capacitor agree, resulting in the control circuit being prompted to output the signal for signaling the regulator circuit ON.
The invention achieves a considerable reduction in the standby current consumption by it firstly signaling all current consumers of the regulator circuit OFF as soon as the design value at the output of the DC/DC converter circuit is attained. Once the regulator circuit has been signaled OFF, monitoring the output voltage is handled by the circuit for signaling the regulator circuit ON/OFF, the comparator of which receivesxe2x80x94unlike the comparator of the regulator circuitxe2x80x94no absolutely precise reference voltage, but instead a voltage briefly applied to the capacitor and defined by the regulator circuit with sufficient accuracy at an output which differs by a predetermined amount from the voltage applied to its other input and characterizing the momentary output voltage. In this arrangement the voltage across the capacitor is always refreshed whenever the comparator of the circuit for signaling the regulator circuit ON/OFF outputs the ON signal. On standby the circuit in accordance with the invention adapts the standby current consumption of the circuit dynamically to the output current required at the output of the DC/DC converter circuit. This enables the DC/DC converter circuit in accordance with the invention, unlike prior art circuits of the kind, to significantly reduce the standby current consumption of the circuit simply and efficiently.